We have created two action method in the C# controller one is to load default select list(First select List, i.e casDropDown), and second method is to get List based on ID of selected Item of first DDL.

In the above code, we have implemented a jQuery function which will be called on Changing first dropdown list value,i.e "Province", on change of it, we are selecting it's ID and then sending it to C# controller Method(getDistricts(int provinceid)) using jQuery Ajax.

Sending ID of first DDL, we are getting list of second dropdown list based on ID of the selected item.

After getting the JSON Result as List of districts we are appending it into HTML(dynamically) using jQuery, hence showing the data based on first dropdown list selected item.

Here is the another solution, just for reference as this question is old, but will help to understand cascading dropdown list easily in MVC using jQuery

First your let's go to your controller, in Controller, GetChildItems is the action method which is called from jquery ajax request to get the desired child dropdownlist items based on the selection of parent

That's it, You are done, based on First dropdown if we select "Year", second dropdown will have "Jan","Feb"....etc in it , if we select "Week", second dropdown will have "Sunday","Monday"...etc as data.